1. Field of the Invention
The present invention relates to an optical printer which converts electrical signal to optical signal to form an image on an instant film.
2. Description of the Prior Art
As shown in FIG. 9 and FIG. 10, in an optical printer of a liquid crystal shutter type, an instant film 19 is fixed on a printer main body 101, an optical head 103 is moved forward/backward relative to the instant film 19, and a photosensitive face of the instant film 19 is exposed by the optical head 103.
FIG. 9 shows a state of the optical printer before the optical head 103 starts to move rearward (direction of arrow F) in order to expose the photosensitive face of the instant film 19. FIG. 10 shows a state of the optical printer after the rearward movement of the optical head 102 has been completed, namely, the exposure on the photosensitive face of the instant film 19 has been completed. The optical head 103 positioned in the state shown in FIG. 10 moves forward (direction Fxe2x80x2 opposed to the arrow F shown in FIG. 9) to return back to its original position (position shown in FIG. 9) and stop. Then, as shown in FIG. 11, the instant film 19 is discharged forward from a film discharge port 104.
A sectional view of this optical printer is shown in FIG. 12, and an enlarged view of a portion H of the sectional view in FIG. 12 is shown in FIG. 13.
As shown in FIG. 14, the instant film 19 used in this optical printer has a photosensitive face 19d which is an upper surface, and which is surrounded by a front end portion 19j, a rear end portion 19m, and left and right side end portions 19a and 19b formed so as to connect the front end portion 19j and the rear end portion 19m. 
A developer accommodating portion 19c is formed in the front end portion 19j with a width D1 which is a non-photosensitive portion of the instant film 19, and a waste developer accommodating portion 19g is formed in the rear end portion 19m with a width D2 which is a non-photosensitive portion of the instant film 19. The developer accommodating portion 19c accommodates liquid developer. The waste developer accommodating portion 19g accommodates waste developer which has been applied for exposure on the photosensitive face 19d. Also, a developer retaining bag 19e made of transparent material is provided on an upper face of the photosensitive face 19d. Developer pouring ports 19h are provided between the developer accommodating portion 19c and the developer retaining bag 19e and developer discharging ports 19f are provided between the developer retaining bag 19e and the waste developer accommodating portion 19g at several portions, respectively.
After the instant film 19 is exposed, the instant film 19 is fed out towards the film discharge port by rotating a pair of developing rollers 106 constituting developing means while nipping the instant film 19 between the pair of developing rollers 106, as shown in FIG. 12 and FIG. 13. In this process, the developer accommodating portion 19c is collapsed by the developing rollers 106 so that the liquid developer flows out of the developer accommodating portion 19c. 
The liquid developer which has flown out of the developer accommodating portion 19c enters in the developer retaining bag 19e where the developer is applied to the- entire photosensitive face 19d of the instant film 19, thereby performing developing processing. The liquid developer in the developer retaining bag 19e is caused to flow rearward according to rotation of the developing rollers 106 to flow in the waste developer accommodating portion 19g through the developer discharging ports 19f. At this time, the developer retaining bag 19e is expanded largely on its rear side of the developing rollers 106 due to fluid resistance generated by flowing of the liquid developer into the liquid discharging ports 19f, as shown with reference numeral 19k in FIG. 13.
When the portion of the developer retaining bag 19e which has been expanded by the liquid developer passes through the nip between the developing rollers 106, it acts as an obstacle so that the conveying speed of the instant film 19 by the developing rollers 106 is reduced at this time. As a result, since the conveying speed of the instant film 19 becomes unstable to change, exposure unevenness occurs on the instant film 19.
An object of the present invention is to suppress load variation to the instant film at a time when the exposed instant film is discharged while developing the instant film to maintain the discharging speed of the instant film constant, in the optical printer, thereby suppressing exposure unevenness on the instant film 19.
An optical printer according to the present invention comprises an accommodating portion for accommodating a photosensitive element, a conveying roller for conveying the photosensitive element from the accommodating portion along a predetermined conveying path, and an optical head for irradiating light on a predetermined position on the photosensitive element, wherein an image is formed on the photosensitive element. Then, the photosensitive element is provided on its photosensitive face side with a non-photosensitive portion with a first predetermined width (D1) extending toward a rear end from an front end in a conveying direction of the photosensitive element and a non-photosensitive portion with a second predetermined width (D2) extending toward the front end from the rear end. A position of a light irradiation on the photosensitive element by the optical head is set within a range from a first point at a distance equal to the first predetermined width (D1) from a center of the conveying roller on the upstream side in the conveying direction and a second point at a distance equal to the second predetermined width (D2) from the center of the conveying roller on the downstream side in the conveying direction.
The optical printer according to the present invention can take the following aspects.
The position of irradiation region is set on the downstream side or the upstream side of the conveying direction with respect to the center of the conveying roller, or it is caused to coincide with an approximate center of the conveying roller in the conveying direction.
The photosensitive element has non-photosensitive portions on both side end portions positioned between the front end side non-photosensitive portion and the rear end side non-photosensitive portion on the side of photosensitive face. The conveying roller is brought in contact with regions corresponding to the non-photosensitive portions on the both side end portions of the photosensitive element to convey the conveying roller.
The conveying roller is rotationally driven at a predetermined rotational speed by driving means and is disposed in opposition to an follower roller with a predetermined pressure relative thereto.
The photosensitive element is an instant film in which liquid developer is accommodated and which can perform self-developing processing. A developing roller is provided for applying the liquid developer to the photosensitive face. The conveying roller and the developing roller are driven by one motor. The conveying roller has a conveying roller driving gear formed coaxially to the rotational shaft of the conveying roller, the developing roller has a developing roller driving gear formed coaxially to the rotational shaft of the developing roller, and both the conveying roller driving gear and the developing roller driving gear are brought to mesh with one intermediate gear to be driven by the one motor.